DESCRIPTION (Adapted from applicant's description): Mucin-type glycoproteins are a major class of apically-secreted/released glycoconjugates of uterine epithelium (UE) of various species, including humans. A series of studies indicates that mucins function as barrier or anti-adhesive molecules. Muc-1 is one of these mucins and is strongly regulated by ovarian steroids in a hormone receptor-dependent fashion. Furthermore, Muc-1 appears to be lost from surface UE during the receptive phase. Recent studies from the investigator's lab indicate that enzymatic removal or genetic ablation of mucin expression converts non-receptive UE to a functionally receptive state in vitro. These observations, along with the observed pattern of mucin expression, are consistent with a role as antiadhesive molecules. Thus, the hypothesis emerges that Muc-1 or mucin removal from surface UE must occur prior to blastocyst attachment. This hypothesis predicts that loss of mucin expression in surface UE serves as a marker of the transition to a receptive uterine state. The investigators will continue their studies of UE mucin expression by studying: 1) steroid hormone regulation of the murine Muc-1 gene; 2) the expression of Muc-1 in human surface UE and UE cell lines and; 3) the function of Muc-1 and other mucins as regulators of embryo attachment in vivo in mice.